As engines, specifically, spark-ignited and diesel engines have increased power output and complexity, the performance requirements of lubricating oils have been increased to require lubricating oils that exhibit a reduced tendency to deteriorate under conditions of use and thereby to reduce wear, rust, corrosion and the formation of such undesirable deposits as varnish, sludge, carbonaceous materials and resinous materials which tend to adhere to various engine parts and reduce the efficiency of engines. Various materials have been included in the lubricating oil compositions to enable the oil compositions to meet the various performance requirements, and these include dispersants, detergents, friction modifiers, corrosion inhibitors, antioxidants, viscosity modifiers, etc.
Dispersants are employed in lubricants to maintain impurities, particularly those formed during operation of an internal combustion engine, in suspension rather than allowing them to deposit as sludge. Dispersant additives for lubricants comprising the reaction products of hydroxy compounds or amines with substituted succinic acids or their derivatives have been described in the prior art, and typical dispersions of this type are disclosed in, for example, U.S. Pat. Nos. 3,272,746; 3,522,179; 3,219,666; and 4,234,435. When incorporated into lubricating oils, the compositions described in the '435 patent function primarily as dispersants/detergents and viscosity-index improvers.
Alkaline earth metal detergents have been included in lubricating oil compositions to suspend degradation products of a motor oil and to neutralize acid products within the oil in the engines. The alkaline earth metals may be calcium, magnesium, barium or strontium, and mixtures of such metals can be used. The alkaline earth metal detergents generally are basic. Alkali metal detergents also have been used in lubricating oil compositions to provide improved detergency.
Alkali metal salts, including basic salts, have been described in the general literature and in patents. For example, Canadian Patent 1,055,700 describes basic alkali metal sulfonate dispersions and processes. More particularly, the patent describes solutions and/or stable dispersions of basic lithium sulfonates, basic sodium sulfonates and basic potassium sulfonates having metal ratios in the range of from about 4 to about 40. In the procedure utilized for the preparation of these overbased sulfonates, the reaction mixture which is contacted with an acidic gaseous material such as carbon dioxide comprises in addition to one or more oil-soluble sulfonic acids or derivatives thereof, one or more alkali metals or metal compounds, one or more lower aliphatic mono- or dihydric alcohols, and one or more oil-soluble carboxylic acids or derivatives thereof. These carboxylic acids include mono- and polycarboxylic acids.
U.S. Pat. No. 3,271,310 (LeSuer) describes metal salts of an alkenyl succinic acid having at least about 50 aliphatic carbon atoms in the alkenyl substituent. The salts include acidic salts, neutral salts or basic salts, and the metals are selected from the class consisting of Group I metals, Group II metals, aluminum, lead, tin, cobalt and nickel. The metal salts of the alkenyl succinic acids are reported to be useful as lubricating additives and may be included in lubricating oils in amounts of from about 0.1% to about 20% by weight. Other additives which may be included in the lubricating oils include, for example, other detergents and dispersants, oxidation-inhibiting agents, corrosion-inhibiting agents, extreme pressure agents, etc.
U.S. Pat. No. 3,312,618 (LeSuer) describes a process for preparing an oil-soluble highly basic metal salt of an organic acid utilizing anhydrous conditions and certain promoters. The organic acids may be sulfonic acids, phosphorus acids, carboxylic acids or mixtures thereof. The carboxylic acids include fatty acids containing at least 12 carbon atoms such as palmitic acid, or cyclic acids such as those containing a benzenoid structure, for example, benzene, an oil-soluble group or groups having a total of at least about 15 carbon atoms and preferably from about 15 to about 200 carbon atoms. The metal compounds utilized to form the metal salts include alkali and alkaline earth metals.
U.S. Pat. No. 4,283,294 (Clarke) describes lubricating oil compositions useful in marine diesel engines, and the compositions comprise in addition to oil, a mixture of a Group Ia metal overbased detergent, a Group IIa metal overbased detergent, and an antioxidant provided that the weight ratio of the overbased detergent mixture to the antioxidant is between 7.5:1 and 50:1. The Group Ia and IIa detergent additives include metal salts of phenols, phenol sulfides, phosphosulfurized polyolefins, organic sulfonates and carboxylic acids. The carboxylic acids are long chain, mono- or dicarboxylic acids such as those wherein the acid radical contains at least 50 carbon atoms per molecule. Thus, the metal salts include salts of long chain succinic acids such as those having molecular weights of 850 to 1200. The antioxidants described in this patent include alkylated hindered phenols, organic amines, organic sulfur compounds, metal thiophosphates, etc. Optional additives in the lubricating oil compositions are dispersants such as polyisobutenyl succinic anhydride-tetraethylene pentamine reaction products.
Lubricating oil compositions containing basic alkali metal salts of sulfonic or carboxylic acids, and carboxylic derivative compositions obtained by reacting substituted succinic acylating agents with at least one amine compound are described in U.S. Pat. Nos. 4,904,401; 4,938,881; and 4,952,238. The carboxylic acids may be either monocarboxylic acids or polycarboxylic acids including dicarboxylic acids such as substituted succinic acids. Suitable carboxylic acids from which useful alkali metal salts can be prepared include aliphatic, cycloaliphatic and aromatic mono- and polycarboxylic acids including naphthenic acids, alkenyl-substituted aromatic acids, and alkenyl succinic acids. The aliphatic acids generally contain from about 8 to about 50, and preferably from about 12 to about 25 carbon atoms. These patents also describe basic alkali metal salts, mixtures of sulfonic acids and carboxylic acids wherein the ratio of equivalents of the carboxylic acid when present to the organic sulfonic acid in the mixture generally is from about 1:1 to about 1:20 and preferably from about 1:2 to about 1:10. The amount of the alkali metal overbased sulfonate or carboxylate included in these oil compositions may range from about 0.01 to about 2% by weight. The oil compositions may contain other desirable additives such as metal salts of dihydrocarbylphosphorodithioic acids, antioxidants, friction modifiers, neutral and basic salts of phenol sulfides, sulfur-containing compounds useful in improving antiwear, extreme pressure antioxidant properties, and neutral or basic alkaline earth metal salt detergents.
U.K. Patent Application 2,062,672 (Zalar) describes additive compositions for lubricating oils which comprise sulfurized alkyl phenol and high molecular weight dispersants. The dispersants are oil-soluble carboxylic dispersants containing a hydrocarbon-based radical having a number average molecular weight of at least 1300 attached to a polar group such as succinic acid or derivative thereof. Generally, the carboxylic dispersants are reaction products of carboxylic acids or derivatives thereof with (a) nitrogen-containing compounds having at least one &gt;NH group, (b) organic hydroxy compounds such as phenols and alcohols, and/or (c) reactive metals or metal-reactive compounds. The carboxylic dispersants may be post-treated with various reagents including sulfur and sulfur compounds, urea, thiourea, aldehydes, ketones, carboxylic acids, epoxides, boron compounds, phosphorus compounds, etc. The carboxylic acids which are utilized in the preparation of the dispersants are referred to as acylating agents. The acylating agent may be prepared by the alkylation of an acid such as maleic acid or anhydride. The alkylating agent may be a polymer containing at least one olefinic bond or a halogen. The number average molecular weight of the polymer is at least 1300 and usually is in the range of about 1500 to about 5000. The ratio of Mw to Mn may be from about 1.5 to about 6 and is usually from 1.5 to about 4. Depending upon the amount of the reactants utilized to form the substituted succinic acids, and depending upon the type of dispersant desired, the mole ratio of the polymer to the maleic acid or anhydride in the reaction mixture may be equal to, greater than or less than 1. In some applications, the dispersant is produced containing an average of at least 1.3 succinic moieties per polymer moiety. Among the reactive metal compounds which may be used to produce the dispersants are alkali metal compounds such as alkali metal hydroxides, carbonates, alkoxides, oxides, etc. The patentees indicate that the lubricating oil compositions may also contain other additives including auxiliary detergents and dispersants, corrosion and oxidation-inhibiting agents, pour point depressing agents, extreme pressure agents, etc.
Engine oil compositions containing increased levels of overbased metallic salts of organic acids are frequently less effective in providing valve-train wear protection as measured by the Sequence V-E test when compared to similar formulations that contain lower levels of such overbased salts. Overbased salts have also been observed to have a detrimental effect on fuel economy as measured by the Sequence VI test.
The Sequence V-E test is a requirement of Military Specifications MIL-L-21260D and MIL-L 46176B and API Classifications SG and SH.
The Sequence VI test is a requirement of API Classification EC and EC-II (energy conserving) oils.
Overbased metallic detergents are used almost universally in engine oils in order to keep parts clean and to neutralize acids formed during combustion of motor fuels.
It is frequently desirable to provide lubricating oil compositions that are suitable for multiple purposes. In one embodiment, it is desirable to provide an engine oil lubricant that meets both gasoline engine lubricant requirements such as those required by API specifications SG and SH and diesel engine lubricant requirements such as API specification CD.
In order to meet API specification CD, increased additive treatments, especially increased treatments of overbased metallic salts, are employed to obtain acceptable Caterpillar 1G2 test results. This test measures piston deposits and wear.
As mentioned hereinabove, when increased amounts of overbased metallic salts are present in an engine oil, wear protection and fuel economy frequently suffer.
Accordingly, it is desirable to provide such overbased metallic detergent-containing lubricating oil compositions that do not display undesirable adverse effects on wear and fuel economy.